The invention relates generally to devices for locating a curvilinear-cut axis about which a veterinarian makes a curvilinear cut producing a proximal and a distal bone sections in connection with an osteotomy procedure. The invention also relates generally to a post-cut step in such procedure that involves correctively rotating about such axis the proximal bone section with respect to the distal bone section. More particularly, the invention concerns a jig for locating such curvilinear-cut axis, and for holding neutrally such two tibial bone sections relative to one another during such corrective rotating.
The invention will be disclosed in the context of performing a tibial osteotomy on a canine but it should be understood that the invention is usable in tibial osteotomy procedures performed on other animals, including human beings. It should also be understood that the invention is also usable for any osteotomy procedure in which a curvilinear cut is made in a bone producing two bone sections, one of which is then correctively rotated relative to the other. Examples of such osteotomy procedures are those that are performed to correct varus or valgus conditions in animals, i.e. animals that are bowlegged or knock-kneed.
By way of background, a proximal tibial osteotomy for leveling a canine's tibial plateau involves a multi-step, cut-and-rotate approach. First, the practitioner, or veterinarian, produces in the proximal tibia a curvilinear through cut that separates it from the metaphysis. Next the veterinarian rotates the metaphysis relative to the proximal tibia a predetermined amount that effectively levels the tibial plateau. Finally, the veterinarian fixes the metaphysis relative to the proximal tibia by suitable means. Such an osteotomy is described in detail in my U.S. Pat. No. 4,677,973 entitled "Proximal, Tibial Osteotomy for Leveling A Tibial Plateau", which issued Jul. 7, 1987, the disclosure of which is incorporated herein by reference.
To begin the above multi-step approach it is necessary for the veterinarian to locate properly the curvilinear-cut axis. If the proper axis is not located then the curvilinear cut will likewise be improper, producing an improper, undesired twist in the canine's leg after the osteotomy is completed. Such curvilinear-cut axis is shown in my U.S. Pat. No. 4,955,888 entitled "Biradial Saw", which issued Sep. 11, 1990, the disclosure of which is also incorporated herein by reference. The biradial saw disclosed in that patent may be used in connection with the above-identified step of producing a curvilinear through cut that separates the metaphysis from the proximal tibia.
Focusing for a moment on the step of locating the curvilinear-cut axis, the environment of the tibial osteotomy makes it difficult to identify a proper axis because the tibia is partially covered by ligaments and other soft tissue.
Ideally, a proper curvilinear-cut axis is approximately normal to a plane that is parallel to the sagittal plane. Because the position and condition of the canine tibia is necessarily partially obstructed during the osteotomy procedure, the veterinarian has a difficult time locating such curvilinear-cut axis. Difficulty in locating the curvilinear-cut axis is also experienced because the canine is positioned during the procedure in such a way that it is difficult to identify a plane parallel to the sagittal plane.
Switching focus to the corrective-rotation step, it is important to prevent certain undesired movement to occur relative to the proximal tibial bone section and the distal (metaphyseal) tibial bone section. Of course rotation about the curvilinear-cut axis is desired, but certain other known translational and rotational movements between the two sections are undesired.
It is therefore desirable to hold neutrally the proximal and distal bone sections during corrective rotation. By holding the sections neutrally applicant means that the sections are held to allow for corrective rotation freely about the curvilinear-cut axis without also compressing the sections together. For a further description of undesired compression between the two sections, see the disclosure in my copending application, Ser. No. 07/822,402, entitled "Tibial Osteotomy Fixation Plate", which disclosure is also incorporated herein by reference. In that application I discuss, among other things, the desirability of selectively compressing/distracting the two bone sections with my novel fixation plate. To ensure that selective compression/distracting is possible when the sections are fixed together, it is important that premature compression/distraction does not take place during corrective rotation. If the sections are held neutrally adjacent each other during corrective rotation no such premature compression/distraction takes place.
Accordingly, it is a principle object of the present invention to provide a jig for locating the curvilinear-cut axis about which a curvilinear through cut is made to separate the metaphysis from the proximal tibia during a procedure referred to as a tibial plateau-leveling osteotomy (TPLO) procedure.
Another object is to provide such a jig that accommodates holding neutrally the proximal and distal tibial bone sections after such curvilinear cut has been made and during corrective rotation of the proximal bone section relative to the distal bone section.
A still further object of the present invention is to provide a jig that will prevent premature compression/distraction of the proximal and distal bone sections while at the same time being usable to hold the bone sections after such curvilinear cut has been made and during corrective rotation of the proximal bone section relative to the distal bone section.
Yet another object of the invention is to provide such jig that is usable in osteotomy procedures for animals of disparate sizes.
Another object is to provide a jig for use with a fixation plate in such TPLO procedure, the jig facilitating accurate and secure relative rotation and fixation of the bone sections, as well as accurate and secure placement and alignment of the fixation plate.